A printer is any printing apparatus which prints on a print medium such as an inkjet printer, a laser printer, a copy machine, a fax machine, etc. Printers include a conventional inkjet printer having a DC printer motor which moves the printhead carrier across the print medium for ejecting ink thereon. The DC printer motor is driven by a motor driver using PI (proportional integral) closed-loop control of the carrier velocity.
A DC adapter, which converts AC power to DC power, is used to power the motor driver. A velocity error is computed as the difference between the measured velocity of the printhead carrier and the desired velocity of the printhead carrier. A digital controller calculates an input to the motor driver which corresponds to the desired motor voltage and which is equal to the sum of a first term which is proportional to the velocity error and a second term which is proportional to the time integral of the velocity error.
A typical desired velocity of the printhead carrier has a desired velocity versus time profile having a trapezoidal shape. The desired velocity of the printhead carrier has a beginning increasing velocity versus time portion, a middle constant velocity versus time portion, and an ending decreasing velocity versus time portion. The initial time is the time at the start of a printhead carrier move, and the final time is the time at the end of the printhead carrier move. The measured velocity of the printhead carrier is obtained using an encoder. The motor driver outputs a control voltage, which is a pulse-width-modulated (PWM) control voltage, to the DC printer motor based on the input to the motor driver.
A potential DC printhead motor stall can occur when the printhead carrier encounters the capping mechanism on the way to the printer sidewall home position of the printhead carrier. When this occurred, the previously-described conventional input to the motor driver would rise to beyond eighty-five percent of the DC adapter voltage. However, the digital controller would limit such input to the eighty-five percent level for thirty milliseconds and then step down to seventy percent for seventy milliseconds to avoid exceeding the thermal limit of the motor driver or the DC adapter or the DC printer motor. Such limits still allowed the printhead carrier to overcome the peak force of the capping device to avoid a DC motor stall and to reach the printer sidewall home position. Thus, such conventional DC printer motor control is a closed-loop control which uses a PI-velocity-error-derived desired motor voltage input to the motor driver before a potential stall is detected and which limits such PI-velocity-error-derived desired motor voltage input as above-described during the potential stall.
Other DC printer motors include those which move the top sheet of print medium from an input tray and those which move a sheet of print medium between print swaths. Potential stalls of such other DC printer motors occur when the sheet of print medium encounters a potential “paper” jam.
What is needed is an improved method for controlling a DC printer motor with a motor driver.